#include <stdio.h>
#include <math.h>

double f(double x);
double df(double x);
void NR(double x0, double tol, int max_itno);
void plotfunction(double x0, double x1, int N);
double min(double a,double b);
double max(double a,double b);

// Driver program
int main() 
{ 
    // Initial values
    double x0 = -4; 
    NR(x0,1e-16,100); 
    plotfunction(-10, 10,1000);
    return 0; 
} 


// Prints root of func(x) with error of EPSILON 
void NR(double x0, double tol, int max_itno) 
{ 
   int i;
   double x,xx0,xx1, h;
   FILE *output;

   output = fopen("nr.dat", "w");//opening file. 

    i=0;
    x=x0;
    xx0=1e16;
    xx1=-1e16;

    while (fabs(f(x)) >= tol&&i<max_itno) 
    { 
        fprintf(output,"%.15f\t%.15f\n",x,f(x));
        xx0=min(xx0,x);

    x = x-f(x)/df(x); 
       i++;
    printf("iteration number: %d \tf(%.15lf) = %.15lf\n",i,x,f(x));
    xx1=max(xx1,x);
    fprintf(output,"%.15f\t%.15f\n",x,0.000);
        fprintf(output,"%.15f\t%.15f\n\n",x,f(x));

    } 
    //plotfunction(xx0, xx1,1000);
     fclose(output);//closing file.

} 


void plotfunction(double x0, double x1,int N)
{ int i;
  double x,dx;
  FILE *output;

      dx=(x1-x0)/N;


output = fopen("function.dat", "w");//opening file. 
 for(i=0;i<N;i++){
    x=x0+dx*i;
fprintf(output,"%.15f\t%.15f\n",x,f(x));
 }
 
 fclose(output);//closing file.

}


// Define function

double f(double x) 
{ 
    double y;

y=cos(x)-x;
    return y;
} 

double df(double x) 
{ 
    double y;

y=-sin(x)-1;
    return y;
} 

double min(double a,double b) 
{ 
if(a>=b){
    return b;
} else return a; 
}

double max(double a,double b) 
{ 
if(a>=b){
    return a;
} else return b; 
}